Carrier-signal selector network



May 12, 1942. B. F. T'YSON 2,283,106

CARRIER-SIGNAL SELECTOR NETWORK Y 1111@ oct. 8, 1940 Patented May i2,1942 UNITED STATES PATENT OFFICE4 2,283,1os I CARRIER-SIGNAL sELEcronNE'rwonx Benjamin F. Tyson, Bayside, N. Y., assignor to llazeltineCorporation, a corporation of Del- Application October 8, 1940, SerialNo. 360,249 7^Claims. (Cl. 178-44) The present invention relates to animproved selector network adapted to translate a plurality of carriersignals and, particularly, to a selector network having a plurality ofpredetermineddistinct band-pass characteristics any one oi which may beselected substantially to the exclusion of the others. Whilev theinvention is of general application, it has particular utility as aselector network between successive stages of intermediate-frequencyamplification of a superhetero-V dyne receiver andwill, therefore, bedescribed in that connection.

Conventional carrier-signal receivers adapted to operate over aplurality of carrier-signal frequency bands generally employ a singlexed intermediate frequency usually between 170 and 470 kilocycles. Thisintermediate frequency provides satisfactory image rejection when thereceiver is operating yin the low-frequency carriersignal bands, butdoes not provide entirely satisfactory image rejection in thehigher-frequency bands, the image rejection becoming increasingly pooras the signal frequency increases.

In order that the image-'rejection characteristic of the receiver shallbe more nearly uniform overl the entire frequency range of the receiver,it is desirable that different intermediate frequencies be employed fordiierent ones of the frequency bands. The selection of a particularintermediate frequency is preferably accomplished by a' switchingarrangement operated simultaneously with the radio-frequency bandselector of the receiver. `In general, an intermediate frequency of 465kilocycles is satisfactory for frequency bands up to 20 megacycles andan intermediate frequency of 2,250 kilocycles is satisfactory for thefrequency bands extending from 20 megacycles up-to 100 megacycles. Theuse of a plurality of intermediate frequencies has the ,additionalimportant advantages that tuning of the receiver is greatly facilitated,the detrimental effect of frequency drift of the local oscillator isminimized,and the larger separation of oscillator frequency and signalfrequency in the higherf-frequency bands makes for greater ease inaligning the receiver by decreasing the drag of' have individual anddifferent band-pass'characteristics suitable to provide the desiredover-all band-pass characteristic for each of the several intermediatefrequencies. Any one of the several intermediate-'frequency selectors isselectively chosen byan appropriateswitching arrangement. The switchingsystems heretofore employed for this purpose have been unduly complexand,l

therefore, relatively expensive 'or have not been altogethersatisfactory in enabling the attainment of the required plurality ofintermediatefrequency amplifier band-pass characteristics.

It is an object of the present invention, therefore, to provide a newand improved selector network which, while of general application, isespecially suitable for use in coupling successive stages ofintermediate-frequency amplification and onewhich avoids one or more ofthe abovementioned disadvantages and limitations of the prior artdevices.

It is a further object of the invention to provide an improved selectornetwork having a plurality of predetermined distinct frequency bandpasscharacteristics any one of which is eflectivev. I

ly selected substantially to the exclusion of the others by theselective operation of a simplified and improved switching system.

In accordance with one embodiment of the invention, aselector networkadapted to translate a plurality of carrier signals comprises a pairof Iinput terminals and a pairl of output terminals,

and a plurality of transformers permanently connected in series andcoupled between the input and output terminals. The selector networkalso includesy means for imparting to each of the transformers apredetermined different Acarrierthe oscillator-tuned circuit on theradio-frequency circuits o f the receiver, o'r vice versa, due toincidental coupling between these circuits.

AFor the purpose of ensuring that the gain of the receiver shall beuniformly high at each intermediate frequency employed, it is desirablethat an individual intermediate-frequency selector be provided for eachone of the several intermediate frequencies. Each selector thus may 5.5;

^ drawing, and its scope will be pointed out in the appended claims. Y

Referring now to the drawing, Fig. 1 is acircuit diagram, partlyschematic, of a complete carrier-signal yreceiver embodying theinvention;

and`Flg. 2 is a circuit diagram representing a modiiied form of theinvention.

Referring now more particularly to Fig. 1, thereV is representedschematically a complete carrier-signal receiver of a conventionaldesign embodying the present invention in a preferred form. In general,the receiver includes a radiofrequency amplier I9 having its inputcircuit connected to an antenna system I2 and having its output circuitconnected to an oscillatormodulator I3. Connected in cascade with theoscillator-modulator I3, in the order named, are anintermediate-frequency amplier |4 more fully described hereinafter, adetector and automatic amplification control or A. V. C. supply I5, anaudio-frequency amplifier |'1 of one or more stages, and a soundreproducer I3. The radiofrequency amplier III and oscillator-modulatorI3 are adapted to operate over a plurality of frequencybands any one ofwhich may be selected by operation of wave band switches conventionallyrepresented at I9 and 23. The A. V. C. bias derived bythe unit I3 isapplied to the input circuit of the radio-frequency ampliner |3, theoscillator-modulator I3, and the intermediatefrequency ampliiler lI4 inconventional manner.

It will be understood that the various units just described may, withthe exception of the intermediate-frequency amplifier I4, be of aconventional construction, the details of which are well known in theart, rendering detailed description thereof unnecessary. Consideringbriefly the operation of the receiver as a whole, and neglecting for themoment the: operation of the intermediate-frequency amplifier I4presently to be described, a desired carrier signal in one of thefrequency bands selected by the band-change switches I9, 29 is receivedand amplied by the radio-frequency amplifier III, converted to anintermediate-frequency carrier signal in the oscillator-modulator |3,amplified in the intermediate-frequency amplifier |4, and detected bythe detector IS thereby to derive the audio-frequency modulationcomponents. The audio-frequency components are, in turn, amplied in theaudiofrequency amplier I1 and are reproduced by the sound reproducer I8in a conventional manner.

. The automatic amplification control supply of unit I operates in aconventional manner to maintain the signal input to the detector withinrelatively narrow limits for a wide range of received signalintensities.

Referring now more particularly to the portion of the system embodyingthe present invention, the intermediate-frequency amplifier |4 includesan input selector network 2| and an output selector network22 eachadapted to translate a plurality of intermediate-frequency carriersignals. These selector networks are essentially similar in constructionand operation and only one, therefore, will be considered in detail;similar circuit elements of each network are desisnated by similarreference numerals except that elements of the network 22 aredistinguished from those of the network 2| by prime numerals. Theselector network 2| has a pair of input terminals 23, 24 and a pair ofoutput terminals 25,

terminals. In order selectively to short-circuit either of the primarywindings 2.9 or 39 thus effectively to short-circuit all but one of thetransformers. there is provided means comprising a single-pole switch 33having a switch blade connected to the junction of the primary windtings 29, 30 and having switch contacts individually connected toopposite terminalsvof the transformer primary windings. There areconnected across the input terminals 23, 24 and the output terminals 25,26 respective condensers 31 and 33. Upon operation of the switch 33 toclose its lower contact, condenser 31 tunes the primary winding 29 oftransformer 21 to a ilrst intermediate frequency while the condenser 33,together with the capacitive effect of the transformer secondary winding32 and a condenser 4| connected in parallel thereto, tunes the secondarywinding 3| of transformer 21 to the same intermediate frequency. Thecondensers 31 and 33 thus comprise capacitive means individuallyconnected across the input and output terminals effectively to tune oneof the' transformers, speciilcally the transformer 21, to the frequencyof a predetermined one of the carrier signals applied to the selectornetwork 2| upon the selection of such one trans-.- former by theswitching means 33. A resistor 33 may be connected across the primarywinding of transformer 21 fto aid in imparting to this transformer apredetermined carrier-frequency band-pass characteristic. Permanentlyconnected across the primary winding 39 and secondary winding 32 oftransformer 23 are respective condensers 43 and 4|. Upon closure of theswitch 33 to its upper contact, the condenser 49 aids the condenser 31in tuning the primary winding 33 of transformer 23 to its own individualintermediate frequency. while the condenser 4I, together with thecapacitive effect of the transformer secondary winding 3| and condenser38. tunes the secondary winding 32 of transformer 23 to the sameintermediate frequency. The

condensers 43 and 4I thus comprise means individual to the transformer23 and effective with the aforementioned capacitive means comprisingcondensers 31 and 33 to tune the latter transformer to the frequency ofan individual one of the applied carrier signals upon selection by theshort-circuiting or switching means 33 of such latter transformer. Thecondensers 31. 33, 40 and 4| and the resistor 39 comprise means forimparting to each of the transformers 21, 23 a predetermined differentcarrier-frequency bandpass characteristic for translating a differentone of the plurality of carrier signals applied to the selector network2|.

'Ihe intermediate-frequency amplifier I4 includes 'a vacuum-tuberepeater 42 having input electrodes coupled to the output terminals 23,23 of the input selector network 2| and output electrodes coupled to theinput terminals 23',v 24 of the output selector network 22. The repeater42 is suitably energized from 'sources of operating potential +B and+Sc. The switches 3'3 and 33' of the respective networks 2| and 22 areconnected for unicontrol operation with the wave band switches I3 and 23of the radio-frequency 23. A plurality of intermediate-frequencytransformers 21, 23 have their respective primary windings 23, 33permanently connected in series acro the input terminals 23, 24 andtheir respective secondary windings 3|, 32 permanently connected inseries across the outputterminals 29, 23 and thus are permanentlyconnected in amplifier I3 and oscillator-modulator I3, as indicated bythe broken line 43.

In considering the operation of the circuit just described, it willbe-assumed that the wave band switches I3 and 23 of the radio-frequencyampliiler |3 and oscillator-modulator |3 are positioned for operation ofthe receiver over la lower-freseries and coupled between the input andoutput quency 110111101' example. the broadcast band .if frequenciesfrom 500 to 1,500 kilocycles, and that the transformers 28 and 28' areconnected in circuit by operation of their respective switches 33 and33' to close their upper contacts. It will further be assumed that theoutput of the oscillator-modulator I3 has a relatively low intermediatefrequency, for example, 456 kilocycles, to which the transformers 28 and28 are tuned. The switches 33 and 33 now short-circuit the respectivetransformer primary windings 28, 23', whereby the intermediate-frequencytransformers 21, 21' are effectively short-circuited and removed fromcircuit. The intermediate-frequency amplifier I4 consequently operatesin conventional manner to translate intermediatefrequency carriersignals within the pass band of the transformers 28, 28' and effectivelyto 31 and 40, the'condensers 38 and 4I may arbisuppress all otherintermediate-frequency carrier signals. The over-all transmissionband-pass characteristic of the amplifier I4* is, under the assumedconditions, determined solely by the.

band-pass characteristics of the transformers 28, 28.

Upon movement of the wave band switches I8 and 20 to select ahigher-frequency band over which the receiver is to be operated, as, forexample, a frequency band above megacycles, the switches 33, 33' aresimultaneously moved,

by virtue of their mechanical connection with the wave band switches, toclose their lower'contacts. The transformer primary windings 38, 3U

are thereupon short-circuited, whereby the transformers 28, 28' areeffectively removed from circuit, and the transformers 21, 21 areconnected in circuit in the intermediate-frequency amplifier I4. At thesame time, the operation of the switch 20 to its new position has theresult that the intermediate frequency now produced'in the output of theoscillator-modulator I3 has a relatively high frequency, for example,2,250 kilocycles, to which the transformers 21, 21' are tuned. Theoperation of the intermediate-frequency amplier I4 is again conventionalin every respect except that it translates intermediate-frequencycarrier signals of the new intermediate frequency and effectivelysuppresses the transmission of all other intermediate-frequency signals.The over-all transmission characteristic of the intermediate-frequencyamplier I4 is now determined solely by the individual band-passcharacteristics of the transformers 21, 21'.

The selector network of the invention thus comprises -two tunedtransformers having primary windings, selected by switches, which areresonant at either of two carrier-signal frequencies and a secondarycircuit which is simultaneously resonant at both these frequencies,thereby to provide two selectable band-pass characteristics havingmaximum transmission at two carrier-signal frequencies. The network alsohas a minimum transmission characteristic at a carrier-signal frequencylying between the two frequencies of maximum transmission. In selectingthe values of the circuit constants of the selector network, the valuesof the transformer primary windings 28 and 30 and the condensers 31 and40 are computed in conventional manner,

'the value of the condenser 31 preferably being made as small aspossible consistent with permissible small changes of capacitanceresulting from tube replacements, temperature variations, etc., in orderthat the voltage-transfer ratio of the transformers 21 and 21' should behigh.

l Having chosen suitable values for the condensers trarily be given thesame respective values and the values Vof inductances of the transformersecondary windings 3l and 32, and the minimum transmission frequency,are given by the following equations:

4- 412f12f3202 I where,

`Ca='the capacitance of ,condenser 4I,

C1=the capacitance of condenser 38,

L3=theinductance of the transformer secondary winding 3l,

L4=the inductance of the transformer secondary winding 32,

f1=the carrier-signal frequency to former 28 is tuned,

fz--the-'frequency of minimum response of the selector network, and

'fa=the carrier-signal frequency to which the transformer 21 is tuned.

Fig. 2 isaJ circuit diagram representing a modiwhich trans- 'fied formof the invention essentially similar to that of the Fig. 1 embodimentexcept that the selector network of this modification is adapted totranslate more than two intermediate-frequency carrier signals. Circuitelements of the' Fig. 2 arrangement corresponding to similar circuitelements of the Fig. l arrangement arc designated by similar referencecharacters and analogous circuit elements by the same reference numeralsdouble-primed. 'In this modification, a transformer 44 has a primarywinding 45 l which is permanently connected in series with the primarywindings 28 and 38 of the respective transformers 21 and 28 across theinput terminals 23, 24 and has a secondary winding 46 which ispermanently connected in series with the secondary windings 3I and 32across 'the output terminals 25, 26 of the selector network. 'I'hetransformer 44 is tuned by a condenser 41 and by a condenserv 48 withother of the capacitive effects of the secondary circuit elements tov anintermediate frequency different from those to which the transformers 21and 28 are tuned. A resistor 49 is connected "across the primary windingtoaid in imparting to transformer 44 a predetermined carrier-frequencyband-passv characteristic. The switch 33" is slightly different from thecorresponding switch of the Fig., 1 arrangement in that it'has a pair ofsegments 5I), 5I which rotate together, each of the segments being ofsufficient length to engage any three adjacent .switch contacts. Theswitch has four equally-spaced contacts 52-55,

`contacts 52 and 55 vbeing individually connected across the inputterminals 23, 24, contact 53 being connected to the junction oftheprimary windings'of transformers 21 and 4,4,.and contact 54 beingconnected to the junction of the primary windings of transformers 44 and.28. The switch 33" is uni-controlled with the wave band switch of thereceiver as indicatedby the broken line 43. Y

The operation of this modification of1 the invention is essentiallysimilar to that of the Fig. 1 embodiment, the switch 33"short-circuiting all but a selected one of the transformer primary totranslate and effectively suppresses the transmission o'f all othercarrier signals. From the foregoing description of the invention, itwill be evident that a selector network embodying the invention has aplurality of predetermined distinct frequency band-pass characteristicsany one of which is eflectively selected substantially to the exclusion`ofthe others by the selective operation of a single switch of simple andinexpensive construction comprising a minimum of switch contacts. Eachof the frequencyband-pass characteristics of the `vselector network maybe adjusted and shaped quite independently ofA other of the kband-passcharacteristics since individual groups of elements provide a givenAband-pass characteristic andA operate quite independently of othergroups of elements of the vselector network.

While the switches 33, 33' and 33" are arranged to short-circuitselected ones of the transformer primary windings, it will be evident toone skilled in the art that, as an alternative andequivalentarrangement, the switches could equally well be arranged toshort-circuit selected ones of the transformer secondary windings.

While there have been described what are at present considered to be thepreferred embodiments of this inventiomitwill be obvious to thoseAskilled in the art that various; changes and modia plurality oftransformers having primary windings permanently connected in seriesacross said input terminals and secondary'windings permanentlyconnected, in series across said output terminals, means for impartingto each of said transformers a predetermined different carrierfrequencyband-pass characteristic for translating a different one of said carriersignals, and a single switch for short-circuiting all but a selected oneof said transformer primary windings effectively to short-circuit allbut oneof said transformers to suppress the transmission between thesaid input and output terminals of all of said carrier signals exceptthe carrier signal which said one transformer is' adapted to translate.

4. A selector network adapted to translate a plurality of carriersignals comprising, a pair of input terminals anda pair of outputterminals, a pair of transformers having primary windings permanentlyconnected in series across said input terminals and secondary windingspermanently connected in series across said output terminals, means forimparting to each of -said transformers a predetermined differentcarrier-frequency band-pass characteristic for translating a differentone of said carrier signals, and a singlepole switch having a switchblade'connected to the junction of one of said pairs ofseries-concations mayl be made therein without departing fromthe'invention, and it is, therefore,'aim'ed in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What is claimed is:

1. Av selector network adapted to translate a plurality'of carriersignals comprising, a pair of input terminals and a pair of outputterminals, a plurality of transformers permanently connected in seriesand, coupled between said input and'output terminals, means for`imparting to each of said transformers a predetermined differentcarrier-frequency band-pass characteristic for translating a differentone of said carrier signals, and a single switch foreffectivelyshortcircuiting all but a selected one of said transformers effectivelyto suppress the transmission between the said input and output terminalsof all'of said applied carrier signals except the carrier signal whichsaid one transformer is adapted to translate. ,A

2. A selector network adapted to translate a plurality of carriersignals comprising, a pair of 'input terminals and a pair` of outputterminals, a plurality of transformers having pri'- mary windingspermanently connected in` series across said input terminals andsecondary windings permanently connected lin series across said outputterminals, means for imparting to each of said `transformers apredetermined different carrier-frequency band-pass characteristic forCil translating a different one of said carrier signals,

and a single switch for effectively short-circuiting all but a selectedone of said transformers efthe said input and output terminals of all ofsaid carrier signals except the carrier signal which fectively' tosuppress the transmissionbetween nected windings and switch contactsindividually connected to opposite terminals thereof, whereby either ofsaid one transformer windings may be selectively l'short-circuitedeffectively to short? circuit one of saidetransformersto suppress thetransmission between the said input and output `terminals of all of.said applied carrier signals except the carrier signal which the otherofsaid transformers is adapted to translate.

5. A selector network adapted to translate a plurality of carriersignals comprising, a pair of input terminals and a pair of outputterminals, -a pair of transformers having primary windings permanentlyconnected in series across said input terminals and secondary windingspermanently connected in series across said output terminals, means forimparting to each of said transformers a predetermineddifferentcarrierfrequency band-pass characteristic for translating al differentone of said carrier signals, and a single switch having a switch bladeconnected to the junction of .said primary windings and switch contactsindividually connected to the op- Y posite terminals thereof, wherebyeither of said primary windings may be short-circuited effectively toshort-circuit one lof said transformers to suppress the transmissionbetween the said linput and output terminals of all of said carriersignals except the carrier signal which said other transformer isadapted to translate.

6. A selector network adapted to translate a plurality of carriersignals comprising, a pair of input terminals and a pair of outputterminals, a plurality of transformers having primary windingspermanently connected in series across said input terminals andsecondary windings permanently connected in series across said outputterminals, means for effectively short-circuiting all but one of saidtransformers, capacitive means individually connected across said inputand output terminals effectively to tune one of said transformers to thefrequency of a predetermined one of said carrier signals upon theselection of said y named capacitive means to tune each of said othertransformers to the frequency of a dif- -ferent one of said carriersignals upon the selection by said short-circuiting means'of others ofsaid transformers.

7. A selector network adapted to translate a plurality of carriersignals comprising, a pair of input terminals and a pair of outputterminals, a. plurality of transformers having primary windingspermanently connected in series across said input terminals andsecondary windings permanently connected in series across said outputterminals, means for eiectively short-circuiting all but a selected oneof said primary windings, ca-

pacitive means individually connected across said input and outputterminals effectively to tune one of said transformers to the frequencyof a predetermined one of 1said carrier signals upon the selection ofsaid one transformer by said lastnamed means, and capacitive meansindividual toeach of the other of said transformers and effec-v tivewith said rst-named capacitive means to tune each of said othertransformers to the frequencyV of a different one of saidcarriersignalsupon the selection by said short-circuiting means ofothers of said transformers.

BENJAMIN F. rTYSON.

